Stirling cycle type engines are well known in the prior art. A Stirling cycle machine is a device which operates on a regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels, wherein the flow of the fluid is controlled by volume changes so that there is a net conversion of heat to work or vice versa. In a typical Stirling cycle engine, operating as a prime mover, heat is supplied to the working fluid at some high temperature Th, when the fluid is in a hot chamber. Part of the heat is converted to work when working fluid, due to the absorbed heat, expands and thereby pushes on a piston, which is coupled to a crank shaft that imparts rotary motion. The working fluid is then displaced by a displacer through a regenerator and forced into a cold chamber, which is at some lower temperature Tl. Thereafter, the working fluid is forced out of the cold chamber by the displacer through the regenerator into the hot chamber; and, as it passes through the regenerator reabsorbs some of the heat previously deposited there. In the hot chamber it again absorbs heat and the cycle of operation repeats itself.
In a Stirling cycle engine operating as a prime mover, the working fluid expansion takes place in the hot chamber, while most of the compression takes place in the cold chamber. As is appreciated by those familar with the art, when the Stirling cycle is used in a hot-gas engine, the working fluid expansion occurs in the hot chamber while the compression of the working fluid, during which heat is rejected, takes place in the cold chamber. In either type machine, the working fluid is shifted between the two chambers through a regenerator by means of a displacer. The motion of the displacer is generally synchronized with the piston motion by means of mechanical linkages which add to the complexity of the machine.
The theoretical maximum efficiency of a hot-gas engine is determined by the following formula: EQU (Th-Tl)/Th
wherein Th denotes the absolute temperature prevailing on the hot side of the engine and Tl the absolute temperature prevailing on the cold side of the engine. Therefore, it is important for satisfactory efficiency to maintain the temperature on the hot side of the engine as high as possible and on the cold side of the engine as low as possible.